Martian water frost : control of global distribution by small-scale processes
This thesis analyzes the small—scale physical processes occurring in the Martian water polar frosts. The small—scale processes are considered from the point of view of how they control the global distribution and behavior of water on Mars. The analysis of the small—scale properties of the surface fr...
| Summary: | This thesis analyzes the small—scale physical processes occurring in the Martian water polar frosts. The small—scale processes are considered from the point of view of how they control the global distribution and behavior of water on Mars. The analysis of the small—scale properties of the surface frost is essential in efforts to find solutions for some outstanding, contradictory observations, to interpret correctly remote sensing observations, to model the surface—frost thermal balance, and to implement the boundary conditions and parameterizations used in the global models of the volatiles' behavior on Mars. Two different problems are investigated in this thesis:
The effect of surface roughness on frost temperature and morphology is studied in Chapter 2 and 3. The investigation of the temperature/roughness feedback leads to the following suggestion: There is a natural tendency of volatile surfaces to develop spontaneously small-scale roughness in a sublimation—dominated environment. The evidence for this claim consists of the model of a rough—surface thermal balance, and of the terrestrial analogs of differential sublimation structures. Such a phenomenon can be tested by the Mars Observer and has important implications for the behavior of water frost on Mars.
Viking Lander 2 winter—frost observations are described in Chapter 4. This study suggests that winter water frost occurred there in two forms: a) thin, almost continuous, early frost, and b) much thicker, patchy, later frost with local cold—trapping of water vapor playing the crucial role. This conclusion is based on the correlation of multiple data sets (from both Viking Orbiter and Lander) and on the combined models of the physical processes occurring on a small scale — below the resolution of remote sensing. The evidence consists of the frost—surface coverage and color transitions, and of the calculation of the vertical and horizontal water—vapor transport near the surface. Again, this phenomenon can be confirmed or rejected by a set of observations from the Mars Observer.
The inherent rough—surface morphology and the frost cold—trapping must be a general property of at least some forms of the seasonal and residual frosts. Both effects must be considered in order to understand the global observations of the Martian frost and the surface environment of Mars in general.
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